The present invention relates generally to fastener-driving tools used to drive fasteners into workpieces, and specifically to combustion-powered fastener-driving tools, also referred to as combustion tools or combustion nailers.
Combustion-powered tools are known in the art, and one type of such tools, also known as IMPULSE® brand tools for use in driving fasteners into workpieces, is described in commonly assigned patents to Nikolich U.S. Pat. Re. No. 32,452, and U.S. Pat. Nos. 4,522,162; 4,483,473; 4,483,474; 4,403,722; 5,197,646; 5,263,439 and 6,145,724, all of which are incorporated by reference herein. Similar combustion-powered nail and staple driving tools are available commercially from ITW-Paslode of Vernon Hills, Ill. under the IMPULSE® and PASLODE® brands.
Such tools incorporate a tool housing enclosing a small internal combustion engine. The engine is powered by a canister of pressurized fuel gas, also called a fuel cell. A battery-powered electronic power distribution unit produces a spark for ignition, and a fan located in a combustion chamber provides for both an efficient combustion within the chamber, while facilitating processes ancillary to the combustion operation of the device. Such ancillary processes include: inserting the fuel into the combustion chamber; mixing the fuel and air within the chamber; and removing, or scavenging, combustion by-products. The engine includes a reciprocating piston with an elongated, rigid driver blade disposed within a single cylinder body.
Upon the pulling of a trigger switch, which causes the spark to ignite a charge of gas in the combustion chamber of the engine, the combined piston and driver blade is forced downward to impact a positioned fastener and drive it into the workpiece. The piston then returns to its original, or pre-firing position, through differential gas pressures within the cylinder. Fasteners are fed magazine-style into the nosepiece, where they are held in a properly positioned orientation for receiving the impact of the driver blade.
Conventional combustion tools have been provided with back pressure release openings located at a lower end of the cylinder adjacent the bumper. It has been found that these openings allow the escape to ambient of air pushed in front of the advancing piston. By removing this trapped air from the cylinder, back pressure on the piston is reduced and the fastener driving power of the piston is increased. However, the reduction of back pressure also means that the piston engages the bumper with greater force. Thus, when standard fasteners are driven into standard substrates, such as plywood and construction grade lumber, the force is largely absorbed by the fastener. However, over time, it has been found that increased impact of the piston on the bumper can cause shock impact-related damage to the tool, particularly when relatively short fasteners are driven, and/or when the fasteners are driven into relatively soft substrates. Such damage includes, among other things, premature component failure due to the excess energy being absorbed by the tool.